A fluoroelastomer is a fluorocarbon-based synthetic rubber. Fluoroelastomers exhibit excellent resistances to heat, oil, solvents and chemicals, especially when compared to non-fluorinated elastomers. Currently, the most widely used fluoroelastomers are copolymers of vinylidene fluoride (VDF) with at least one other fluorinated co-monomer such as tetrafluoroethylene (TFE) and hexafluoropropylene (HFP). Apart from these well-known fluoroelastomers, other fluoroelastomers were developed for particularly demanding applications. For example, fluoroelastomers based on copolymers of TFE and perfluoro(methyl vinyl ether) (PMVE) have been developed that are resistant to prolonged exposure to temperatures as high as 280° C. Another special purpose fluoroelastomer, based on copolymers of TFE and propylene, has high vapor resistance and excellent processability.
These fluoroelastomers have many desirable properties and are particularly useful for applications that demand resistance to very high temperatures. However, their usefulness at low temperatures is limited by their usually relatively high glass transition temperature (Tg). A high Tg is generally regarded as an indicator that a fluoroelastomer is inflexible at low temperatures. When the temperature drops below the Tg of a particular fluoroelastomer, the fluoroelastomer becomes stiff or brittle and non-elastomeric. Fluoroelastomers having low glass transition temperatures are able to maintain elastomeric properties at low temperatures.
U.S. Pat. No. 4,513,128 discloses a fluoroelastomer which comprises tetrafluoroethylene/perfluoro(methyl vinyl ether) copolymers. This fluoroelastomer has a low Tg in the range of −15° C. to −100° C. when it contains 3 to 50 mole percent of copolymerized perfluorovinylpolyether (PVPE) of the following formula: CF2═CFO[CF2CF(CF3)O]nRf1, wherein Rf1 is a C1-12 perfluoroalkyl group and n is an integer between 3 to 30. Tetrafluoroethylene tends to be unstable and to decompose to C and CF4, and is prone to form explosive peroxides when in contact with air while, and perfluorovinylpolyether (PVPE) monomers are extremely costly.
Thus, there remains a need to develop novel fluoroelastomers that include relatively low cost and non-hazardous monomers, yet have a low glass transition temperature. The present invention addresses this need.